Carob leaf and pomegranate peel extracts may help reduce the incidence of "soapy olive" disease

Anthracnose is considered one of the most significant diseases affecting olive trees. Popularly known as “soapy olive” due to the appearance of fruit affected by it, this disease, caused by various fungal species of the genus Colletotrichum, significantly reduces yields and undermines oil quality, particularly during epidemic years.

Now, a new international study has identified two bioprotectants as potential candidates to mitigate the damage wrought by this disease: plant extracts derived from carob leaves and pomegranate husks. These raw materials, previously viewed as plant or agri-food industry waste, are now emerging as promising alternatives to traditional fungicides, thereby contributing to the biocircular economy.

According to the results of the study, conducted by the Department of Agronomy at the University of Cordoba (DAUCO) in collaboration with the Polytechnic Institute of Bragança (Portugal), both extracts significantly reduce the production and germination of the fungus’s conidia, and also prevent the formation of appressoria, “two key structures the fungus uses to disperse and initiate infection in the plant,” emphasized Begoña Antón, the lead author of the study. Furthermore, the study’s findings highlight that the preventive foliar application of both extracts—especially carob—activates the plant’s defense mechanisms linked to its antioxidant response. This application also increases the production of certain phenolic compounds that help strengthen the plant’s natural resistance to the pathogen.

A study conducted under controlled conditions that opens new doors

To achieve these results, the research team conducted in vitro tests and bioassays on both individual olives and olive seedlings in controlled environment chambers. In fact, in this latest trial, researchers confirmed that carob leaf extract can reduce the disease’s incidence by 35%. “Although this percentage is lower than that achieved with a traditional copper-based fungicide, it represents an important step forward in optimizing the effectiveness of these compounds,” stated Carlos Agustí, the principal investigator on the study.

This study opens up new avenues for the development of sustainable anthracnose control strategies using bioprotectants, which could reduce the need for fungicides, as their use is increasingly restricted by the European Union. However, several important steps still need to be taken to achieve this, including testing how these bioprotectors perform in field conditions, where environmental and biological factors are more variable and complex, and studying the feasibility of scaling them up industrially if their effectiveness is confirmed.